1. Field of the Invention
This invention relates to an apparatus and a method for individually separating particles to be examined in a sample fluid in which fine particles, such as cells or the like, are suspended, and also to an apparatus and a method for measuring the separated individual particle by an optical method or the like.
2. Description of the Prior Art
Heretofore, as a method for individually separating a large number of particles in a particle-suspending fluid, such as a blood sample or the like, a sheath flow method as shown in FIG. 14 has been generally known. In this method, a particle-suspending fluid and a sheath fluid are pressurized by respective pressurizing devices, and the particle-suspending fluid flows in a state surrounded by the sheath liquid. The particle-suspending fluid is hydrodynamically converged into a narrow flow, and the particles are separated and flow one by one in a row.
An apparatus for analyzing or sampling cells, in which a sample, such as blood or the like, is prepared and respective cells in the sample separated by the sheath flow method are measured by an optical method or the like, has been practically utilized in the name of a flow cytometer or a cell sorter.
FIG. 14 shows an example of the configuration of a flow cytometer, which irradiates energy for measurement such as a light beam from a light source 24 onto respective cells separated by the sheath flow method and flowing in a row within a flow cell, and performs photometry of an optical reaction due to the light irradiation onto the cells such as scattered light and fluoresence issued from the cells by detectors 25 and 26. A signal processing unit 29 calculates the kind, size and the like of the analyzed particle according to an output of the photometry.
The basic principle of the cell sorter has been explained in, for example, U.S. Pat. Nos. 3,380,584, 3,710,933 and 3,826,364. FIG. 15 shows an example of the basic configuration of a cell sorter. A cell-suspending fluid, such as blood or the like, is introduced into a nozzle by an external pressurizing apparatus, and a laminar flow composed substantially of the cell-suspending fluid is produced within the nozzle by the sheath flow principle. A jet stream of the cell-suspending fluid having an average diameter of 15-20 .mu.m is discharged in the air from an orifice (having a diameter of 70-100 .mu.m) disposed at the nozzle outlet. Exciting light from a light source 24 is projected onto the jet stream discharged into the air at a position about 100-200 .mu.m from the front end of the nozzle. When the exciting light is projected onto a cell previously subjected to fluorescent staining, scattered light and fluorescence are issued from the cell, are detected by the detectors 25 and 26, and are converted into electric signals. Since the nozzle is vibrated by a vibrator 21 with a frequency of about 40 kHz (kilohertz) by the control of a vibrator circuit 27, the jet stream discharged from the orifice is converted into uniform liquid drops at a position a few mm lower than the front end of the nozzle. In accordance with whether or not a signal detected from the cell satisfies predetermined conditions, the signal is transmitted from a signal processing unit 29 to a charging circuit 28, from which a charging signal is supplied to the nozzle in synchronization with the liquid-drop formation to slightly charge a liquid drop. While the charged liquid drop containing the desired cell passes between two electrodes 22 and 23 producing a strong electric field, the liquid drop is deflected and distributed in the right or left direction by static electricity in accordance with the kind or the like of the cell, and is collected in one of separate test tubes.
In the sheath flow method utilized in the above-described flow cytometer or cell sorter, since the cell-suspending fluid and the sheath fluid are guided to the nozzle by pressurizing the respective fluids by the pressurizing systems, piping and pressurizing devices, such as pumps or the like, are needed for that purpose. Hence, this method has the disdavantages of needing a large apparatus and complicated control system.
In the sheath flow method, flow rate is determined by pressurizing forces for the cell-suspending fluid and the sheath fluid, and the time interval for the separation of particles is determined by the flow rate and the degree of dilution of the cell-suspending fluid. It is difficult to freely set the time interval, that is, the timing for the separation over a wide range. The method also has the disadvantage that a certain time is needed from the formation of the flow to the start of the separation and from the stoppage of the flow to the stoppage of the separation, and the sample therefore flows uselessly.
Furthermore, it is difficult to provide a small apparatus, and it is also difficult to provide a plurality of apparatuses in parallel in high density to increase processing capability.